Cathode-ray tube for displaying coloured pictures

ABSTRACT

A television display tube of the shadow-mask type, comprising three electron guns having parallel axes; the last electrode of each electron gun has the shape of a cylindrical sleeve and the electron gun the axis of which do not coincide with the main axis of the tube have an eccentric last electrode.

United States Patent Linssen Sept. 16, 1975 1 1 CATl-lODE-RAY TUBE FOR DISPLAYING COLOURED PICTURES [56] References Cited [75] Inventor: l-lenricus Wilhelmus Maria Linssen, UNITED STATES PATENTS Emmasmge], Emdhovem 2,850,658 9/1958 Allwine 313/70 0 Netherlands 3,772,554 11/1972 Hughcs 313/70 c [73] Assignee: U.S. Philips Corporation, New

York, NY. Primary ExaminerR. V. Rolinec Assistant Examiner-E. R. LaRoche Filed 1973 Attorney, Agent, or FirmFrank R. Trifari; George B. [21] Appl. N0.: 418,582 Berka [30] Foreign Application Priority Data [57] ABSTRACT Dec. 16, 1972 Netherlands 1. 7217179 A television display tube of the shadow-mask type, comprising three electron guns having parallel axes; [52] US. Cl. 313/409; 313/356; 313/412; the last electrode of each electron gun has the shape 313/414 of a cylindrical sleeve and the electron gun the axis of [51 Int. Cl. H01j 29/50 which do not coincide with the main axis of the tube [58] Field of Search 313/69 C, 70 R, 70 C, 82 R, have an eccentric last electrode.

4 Claims, 4 Drawing Figures PM'ENIH} SEP 1 S 5973 SHEET 1 OF 2 CATI-IODE-RAY TUBE FOR DISPLAYING COLOURED PICTURES The invention relates to a cathode-ray tube for displaying color pictures and comprising in an evacuated envelope: three electron guns the axes of which are parallel to the main axis of the tube for producing three electron beams, a color selection electrode comprising a multitude of apertures, a display screen having three patterns of regions luminescing in different colors, and means for converging the three electron beams so that they intersect each other near the color selection electrode, which electron beams each are assigned to one of the said patterns by means of the color selection electrode, which electron guns each comprise at least a cathode, a control grid and an anode and furthermore a last electrode taken from the cathode which has the form of a mainly cylindrical sleeve, at least two of the said electron guns having an axis which is ecentric relative to the main axisof the tube.

Such a cathode-ray tube is known from the US. Pat. No. 3,01 1,090. In order to converge the three electron beams so that they intersect each other near the color selection electrode it is furthermore known to cause the axes of the three electron guns to intersect each other in a point in the center of the colour selection electrode. The said US. patent states a drawback of this that the guns have to be positioned very accurately in the tube. Another drawback is that the electrodes of the three guns are assembled on three assembling pins which thus have to enclose a very accurely determined angle relative 'to each other. In order to be able to subsequently remove the set of three assembled electron guns from the three assembly pins, it'is necessary for said pins to be secured in a jig so as to be detachable, as a result of which their mutual angle becomes less accurate due to detrition.

It is the object of the invention to mitigate the said drawbacks, and the invention furthermore provides a very simple construction for converging three electron beams from three assembled electron guns which operate independently of each other and the axes of which are parallel. g

According to the invention, a cathode-ray tube of the type mentioned in the preamble is characterized in that the last electrode of each electron gun which is eccene tric relative'to the main axis of the tube has an axis which is eccentric relative to the axis vof the assigned electron gun in a plane passing through the main axis of the tube and the axis of the assigned electron gun and at a larger distance from the main axis of the tube than the axis of the electron gun and that the said last electrode hasan inner diameter which is at least equal to the largest inner diameter of any other electrode of the electron gun increased by twice the distance between the axes of the last electrode and the electron gun.

Due to the eccentrically arranged last electrodes, convergence is obtained in a simple manner so that the axes of the three electron guns can be parallel and the assembly pins for assembling the three guns can be rigidly secured in a jig. By choosing the inner diameter in the stated manner to belarger it is achieved that the last electrode which is mounted first on the assembly pin can easily be moved over the thinner pin portions destined for the other electrodes, while the assembled gun can still removed from the pin'because, no reentrant pin poition'is formed.

The invention relates in particular to sucha cathoderay tube having-three electron guns the axes of which are in one plane and one axis coincides-with the main axis of the tube which is characterized in that the axis" of the last electrode of the electron gun-the axis of which coincides with the main axis of the tube, coincides with the axis of the electron gun.

The invention also relates to a cathodeway tube having three guns in a triangular arrangement which is characterized in that the last electrodes of the three electron guns have the same inner diameter.

The invention will be further described in greater detail with refe'rence to the accompanying drawing, "of which FIG. 1 shows a cathode-r'ay'tube according to the invention,

FIG. 2 shows the three electron guns of the tube of FIG. 1 in their mutual arrangement,

FIG/ 3 shows the three electron guns of a known cathode-ray tube during assembly, and

FIG.-4 sho'ws the three electron guns of a cathode-ray tube according to the inventionduringassembly.

The tubeshown inFIG. 1 comprises in an evacuated glass envelope 1 a set of electron guns 2, a colour'selection electrode 3 and a display screen 4. Outside the envelope l of the tube are shown a set of deflection coils 5 which serve for the deflection across the display screen 4 of the electron beams produced by the electron guns 2, In. known manner, which need not befurther explained, one of the electron beams impinges, via the apertures 6 in the colourseleetion electrode 3,'only upon regions having red luminescing phosphor of the display screen 4, the second electron beam impinges only upon regions having green phosphor and the third electron beam impinges only upon regions having blue phosphor. The main axis of the tube is denoted by the reference numeral 7. I g V g Y I FIG. 2 shows the set of electron guns 2 in greater detail. It comprises three electron guns I0, 20 and 30, the axes 17, 27 and 37 of which are parallel to each other. The electron gun l0. comprises a cathode l2 having a filament l l, a control grid 13, and anode 14, a focusing electrode 15 and an accelerating electrode 16. Thecorrespondingelectrodes of the electron gun 20 are denoted by reference numerals 21 ;to 26. The corresponding electrodesof the electron gun 30 aredenoted by reference numerals 31 to 36. In a manner not shown the electron guns 10, 20 and 30 are secured to glass supporting rods so as to be immovable relative to each other by means of connection lugs sealed in the supporting rods. As shown in FIG. 2, the axes 17, 27 and I 37 of the electron guns are in one plane. In another embodim ent which needs no further explanation the electron guns 10, 20 and 30 have a thriangular arrangement, that is to say that the points of intersection of the axes of the electron guns with a plane normal to the main axis of the tube form an equilateral triangle having the point of intersection of the main axis of the tube as center of gravity.

As shown in FIG. 2, the acceleration electrodes 16 and 36 have a slightly larger diameter than the focusing electrodes 15 and 35, while the axes l8 and 38 of the electrodes 16 and 36 are also eccentric relative to the axes l7 and 37. The electric field between the electrodes I5 and 16 and 35 and 36, respectively, thus has such a shape that the electron beams produced by the electron guns and 30 are deflected towards the electron beam produced by the electron gun 20. The three beams intersect each other at the area of the colour selection electrode 3. In the case of three electron guns in a triangular arrangement, the electron beams are deflected towards each other in a quite analogous manner. The stated eccentricity is so small that the devia tion from the rotational symmetry of the electric field between the electrodes and 16 and 35 and 36, respectively, has a detrimental influence on the structure of the electron beams individually. The largest inner diameter of the electrodes 15, and 35 is 7.6 mm. The inner diameter of the electrode 26 is also 7.6 mm. The inner diameter of the electrodes 16 and 36 is 8.2 mm. The eccentricity of the electrodes 16 and 36, that is to say the distance between the axes l7 and 18 and 37 and 38, respectively, is 0.3 mm. As already noted, the axes 27 and 28 coincides. In the case of three elec tron guns in a triangular arrangement, all the acceleration electrodes are eccentric relative to the corresponding focusing electrodes.

FIG. 3 shows three electron guns of a known cathoderay tube during their assembly. Three assembly pins 41, 42 and 43 are secured in a block 40. The axes of the pins 41 and 43 intersect each other in a point on the axis of the pin 42. For clarity, the angle between the axes of the pins 41 and 42 and 42 and 43, respectively, is shown to be larger than is the case in practice. The diameter of the pins 41, 42 and 43 becomes smaller stepwise towards their end. FIG. 3 shows how this is used to assemble the electrodes of an electron gun on a pin. Temporarily provided spacing members 44 are also used. In FIG. 3, the electron gun on the pin 42 is still to be assembled. After providing all the electrodes, the electrodes which are provided with connection strips not shown are sealed in glass supporting rods by means of said strips. The three electron guns then form one assembly and it is obvious that, for being able to remove the pins 41, 42 and 43 from the guns, it is necessary first to remove the pins 41, 42 and 43 from the block 40, only after which they can be withdrawn from the guns. This requires a large number of operations and in addition produces detrition so that the angle between the pins 41, 42 and 43 becomes inacurate.

FIG. 4 shows three electron guns of a cathode-ray tube according to the invention during their assembly. Three assembly pins 51, 52 and 53 are secured in a block 50. The axes of the pins 51, 52 and 53 are parallel. The diameter of the pins 51, 52 and 53 becomes smaller stepwise towards their ends. In this case also,

temporarily provided spacing members 54 are used. After providing all the electrodes. the electrodes which are provided with connection strips not shown are sealed in glass supporting rods by means of said strips. The three electron guns then form one assembly and it is obvious that they can be collectively removed from the assembly pins 51, 52 and 53, said assembly pins remaining secured in the block 50.

What is claimed is:

1. A cathode-ray tube for displaying color pictures comprising in an evacuated envelope: three electron guns the axes of which are parallel to the main axis of the tube for producing three electron beams, a color selection electrode comprising a multitude of apertures, a display screen having three patterns of regions luminescing in different colors, means for converging the three electron beams so that they intersect each other near the color selection electrode, each of said electron beams being assigned to one of the said patterns by means of the color selection electrode, each of said electron guns comprising a set of successively arranged electrodes including at least a cathode. a control grid, an anode and an additional last electrode which has the form of a substantially cylindrical sleeve. at least two electron guns having respectively, a center axis which is eccentric relative to the main axis of the tube, the last electrode of each of said two eccentric electron guns having a center axis which is eccentric relative to the center axis of the assigned electron gun in a plane through the main axis of the tube and the center axis of the assigned electron gun and at a larger distance from the main axis of the tube than is the axis of the assigned electron gun, and said last electrode having an inner diameter which is larger than the largest inner diameter of any other electrode of the assigned electron gun.

2. A cathode-ray tube as claimed in claim 1, having three electron guns the axes of which are in one plane and the center axis of one gun inclusive said last electrode coincides with the main axis of the tube.

3. A cathode-ray tube as claimed in claim 1 and having three electron guns in a triangular arrangement, wherein the last electrodes of the three electron guns have the same inner diameter.

4. A cathode-ray tube as claimed in claim 1, wherein the inner diameter of the last electrode assigned to each of the two eccentric electron guns is equal at least to the largest inner diameter of the corresponding electron gun increased by twice the distance between the axes of the last electrode and the electron gun. 

1. A cathode-ray tube for displaying color pictures comprising in an evacuated envelope: three electron guns the axes of which are parallel to the main axis of the tube for producing three electron beams, a color selection electrode comprising a multitude of apertures, a display screen having three patterns of regions luminescing in different colors, means for converging the three electron beams so that they intersect each other near the color selection electrode, each of said electron beams being assigned to one of the said patterns by means of the color selection electrode, each of said electron guns comprising a set of successively arranged electrodes including at least a cathode, a control grid, an anode and an additional last electrode which has the form of a substantially cylindrical sleeve, at least two electron guns having respectively, a center axis which is eccentric relative to the main axis of the tube, the last electrode of each of said two eccentric electron guns having a center axis which is eccentric relative to the center axis of the assigned electron gun in a plane through the main axis of the tube and the center axis of the assigned electron gun and at a larger disTance from the main axis of the tube than is the axis of the assigned electron gun, and said last electrode having an inner diameter which is larger than the largest inner diameter of any other electrode of the assigned electron gun.
 2. A cathode-ray tube as claimed in claim 1, having three electron guns the axes of which are in one plane and the center axis of one gun inclusive said last electrode coincides with the main axis of the tube.
 3. A cathode-ray tube as claimed in claim 1 and having three electron guns in a triangular arrangement, wherein the last electrodes of the three electron guns have the same inner diameter.
 4. A cathode-ray tube as claimed in claim 1, wherein the inner diameter of the last electrode assigned to each of the two eccentric electron guns is equal at least to the largest inner diameter of the corresponding electron gun increased by twice the distance between the axes of the last electrode and the electron gun. 